[U-Boot] [PATCH 12/12] riscv: Add QEMU virt board support

[Bin Meng]

Hi Lukas,

On Wed, Sep 5, 2018 at 5:37 PM Auer, Lukas
<lukas.auer at aisec.fraunhofer.de> wrote:
>
> On Wed, 2018-09-05 at 10:34 +0800, Bin Meng wrote:
> > Hi Rick,
> >
> > On Wed, Sep 5, 2018 at 9:27 AM Rick Chen <rickchen36 at gmail.com>
> > wrote:
> > >
> > >  > > From: Auer, Lukas [mailto:lukas.auer at aisec.fraunhofer.de]
> > >  > > Sent: Wednesday, September 05, 2018 5:53 AM
> > >  > > To: bmeng.cn at gmail.com
> > >  > > Cc: Rick Jian-Zhi Chen(陳建志); u-boot at lists.denx.de
> > >  > > Subject: Re: [U-Boot] [PATCH 12/12] riscv: Add QEMU virt board
> > > support
> > >  > >
> > >  > > On Tue, 2018-09-04 at 17:31 +0800, Bin Meng wrote:
> > >  > > > Hi Lukas,
> > >  > > >
> > >  > > > On Tue, Sep 4, 2018 at 5:39 AM Auer, Lukas
> > >  > > > <lukas.auer at aisec.fraunhofer.de> wrote:
> > >  > > > >
> > >  > > > > On Thu, 2018-08-30 at 00:54 -0700, Bin Meng wrote:
> > >  > > > > > This adds QEMU RISC-V 'virt' board target support, with
> > > the hope
> > >  > > > > > of helping people easily test U-Boot on RISC-V.
> > >  > > > > >
> > >  > > > > > The QEMU virt machine models a generic RISC-V virtual
> > > machine
> > >  > > > > > with support for the VirtIO standard networking and
> > > block
> > >  > > > > > storage devices.
> > >  > > > > > It has CLINT, PLIC, 16550A UART devices in addition to
> > > VirtIO
> > >  > > > > > and it also uses device-tree to pass configuration
> > > information
> > >  > > > > > to guest software. It implements RISC-V privileged
> > > architecture
> > >  > > > > > spec v1.10.
> > >  > > > > >
> > >  > > > > > Both 32-bit and 64-bit builds are supported. Support is
> > > pretty
> > >  > > > > > much preliminary, only booting to U-Boot shell with the
> > > UART
> > >  > > > > > driver on a single core. Booting Linux is not supported
> > > yet.
> > >  > > > > >
> > >  > > > >
> > >  > > > > For your information and to avoid duplicate work, I am
> > > working on
> > >  > > > > a patch set that improves RISC-V support in u-boot. I am
> > > currently
> > >  > > > > able to boot Linux on a multi-core setup in QEMU, but they
> > > are not
> > >  > > > > quite ready to submit yet.
> > >  > > > >
> > >  > > >
> > >  > > > This is great! My next step is to work on virtio driver
> > > support in
> > >  > > > U-Boot as qemu-riscv virt machine has these devices but we
> > > don't
> > >  > > > have corresponding drivers in U-Boot. Then I will try to
> > > boot Linux
> > >  > > > after that. Good to hear you already boot Linux with qemu-
> > > riscv!
> > >  > > > Have you already supported virtio drivers in your port? If
> > > yes, I
> > >  > > > will just hold on and wait for your patch series :-)
> > >  > > >
> > >  > >
> > >  > > Hi Bin,
> > >  > >
> > >  > > Support for the virtio devices would be great! I don't support
> > > them in
> > >  > > my port, I can only boot a kernel image from RAM.
> > >  > > I only have a driver for the clint0 (core local interrupt
> > > controller),
> > >  > > which I need for software interrupts to other cores and as a
> > > timer.
> > >  > > Software interrupts also work over the supervisor binary
> > > interface
> > >  > > (SBI), which allows u-boot to run in supervisor mode with bbl
> > > running
> > >  > > in machine mode to handle the SBI calls.
> > >  > >
> > >
> > > Hi Bin and Auer
> > >
> > > I have already boot bbl run in S-mode and riscv-linux in M-mode via
> > > u-boot from SD card or FLASH.
> > > It mean after booting riscv-linux, u-boot will be dead. And no
> > > matter
> > > about kernel.
> > > Please refer to doc/README.ae350
> > >
> >
> > Thanks for pointing out the doc for ae350. I just read it, and have
> > one question. There is a chapter in that doc "Boot bbl and riscv-
> > linux
> > via U-Boot on QEMU", yet I don't see what QEMU command is invoked.
> > Can
> > you please clarify? AFAIK mainline QEMU does not have support to
> > ae350
> > board. Also there is no instructions on how bbl was built. Is that
> > the
> > mainline bbl that can work on every riscv board? I doubt that.
> >
> > > May I figure out more clearly what are you going to do ?
> > > What are you going to do is let u-boot run in S-mode and boot bbl
> > > and
> > > riscv-linux in M-mode, right ?
> >
> > I want to use U-Boot to directly boot Linux, but seems Lukas is using
> > bbl for SBI implementation.
> >
>
> Hi Bin,
>
> I don't really need bbl to run u-boot. I use it for Linux, which
> expects the SBI to be present.
>
> > > It mean after booting bbl and riscv-linux, u-boot will still alive
> > > and
> > > handle SBI calls and somethings in S-mode.
> > >
> > > Or u-boot is going to replace the role of bbl ?
> > >
> >
> > That's my plan. I don't see a need to use bbl which is quite feature
> > limited.
> >
>
> That's a good idea! At the very least, all the device initialization in
> bbl should be moved into u-boot.
> I do think a bootloader-independent SBI implementation makes sense
> though. That way all bootloaders can use the same implementation, which
> should make adding new SBI calls easier.

But I doubt we can have a generic SBI implementation. At least the
console I/O SBI call can vary from board to board due to different
UART devices are used.

Regards,
Bin